<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <script src="https://cdn.bootcss.com/jquery/3.4.1/jquery.js"></script>
    <title>Document</title>
</head>

<body>
    <div id="test">hello world</div>
    <button id="btn">切换</button>
    <script>
        /*  var btn=document.getElementById("btn");
        var test=document.getElementById("test");
        btn.onclick=function(){
            var value=test.style.display;
            console.log(value);
            value=="block"?test.style.display="none":test.style.display="block"
        }    */

        $("#btn").click(function () {
            // is(':visible') 判断一个元素是否显示
            var isShow = $("#test").is(":visible")
            console.log(isShow);
            if (isShow) {
                $("#test").hide();
            } else {
                $("#test").show();
            }
        })
    </script>
</body>

</html>